Program control receiver



Jan. 8, 1946. w. R. KoH

PROGRAM CONTROL RECEIVER Filed July 24, 1942 Para@ Jee-@194,6 t

Winfield R. Koch, Haddoniieid, N. J., signor to I Radio Corporation ofAmerica, a corporation of Delaware A I Application July 24, 1942, SerialNo. 452.5173

(CL 25o-20) i claim.

My present invention relates to program control systems, and moreparticularly .to a frequency j modulation communication systembemploying program-selective control tones.

It is often desired on the part of the receiver operator, especially inthe broadcast band, to cut out receiver reproduction during announcementperiods. This type of program control is of especial desirability duringmusic program transmission. Further, the broadcast listener oftenobjects to the fact that speech-music control 1 switches, such asacoustic compensation and fidelity control switches, must be operatedmanually and at the receiver control panel. It would be highly desirableto provide a method of automatically monitoring the program arriving atthe broadcast `receiver so as to secure the aforementionedcharacteristics. Frequently modulation of the present day type lendsitselfI to such monitormg It may be stated to be one of the main objectsof my present invention to provide a radio communication systemwhereln acontrol, or monitor, tone is transmitted along with modulation del airedto be discriminated against at the receiver,

and the control tone being utilized at the receiver to eiiect one ormore control functions with respect to the modulation on the receivedcarrier.

Another important object of this invention is to provide a method ofautomatically preventing receiver response during -announcement periods.of a program broadcast; a special monitor tone being included on thecarrier during such periods.

' Another object of my invention is to providev a broadcast -receiverwherein the listener lis permitted to hearonly announcements, such asnews bulletins, and not the musical program. l

Another object of my invention is `to provide automaticacoustic'compensation control and/or fidelity control at a broadcastreceiver in response to the reception of aspecial monitor tone ofsuperaudible frequency. v

Yet another object of my invention is to providel a frequency modulationsystem ,wherein a super-audible monitor tone is included inthemodulation during such periods of transmission when a particular type ofprogram control is de- Stili' other lobjects are.`to improve generallythe mciency and reliability of program control sys,-

tems. and more `especially to provide such control systems 'in frequencymodulation receivers.

The novel features which I believe tob'e characteristic of my inventionareset forth with particularityin the appended claims; the invention`tions whereby my itself. however, as to'both its organization andmethod of operation will best be understood by 'reference to thefollowing description taken in connection with the drawing in` which Ihave indicated diagrammaticaliy several circuit organizaeect. l In thedrawing: Fig. 1 schematically shows an FM (frequency modulated carrierwave) transmitter system embodyingthe invention; and

, Fig. 2 shows an FM receiver employing the irlvention.

Referring now to Fig. l, there is showna transmitting system of the FMtype. The generic term angular velocity-modulated carrier wave is usedherein to denote that either frequency, or phase, modulation may beemployed. The present system of control with a super-audible monitortone lends itself particularly to high deviation range FM communication.lIn the latter the master oscillator l operates at some carrierfrequency in the assigned ultrahigh frequency band of 42 to 50megacycles (ma). The frequency modulator 2 is usually an electronicreactancedevice which is connected across the oscillator tank circuit.to vary the oscillator frequency with respect to a center frequencywhich is the unmodulated car-l rier frequency value. Themagnitude of theelec-H tronic reactance is varied bythe applied modulation.

Thus, the program microphone 3` feeds the modulation amplifier 4 withthe usual music or other audible program material. The switch 6-5 beingclosed. the amplified modulation energy is fed through a.furtherlampliie'r l to the reactance tube 2. The latter is soconstructed that the carrier frequency is deviatedk in accordance withthe modulation amplitude; the rate of deviation is a function of theymodulation frequencies per se. In the presently-assigned FM band thechannel width is 200 kilocycles (ka), but the transmitter actuallydeviates the carrier a maximum of kc.

. either side of the transmitter mean frequency.

During the course of a program, such as music. there will be announcing.periods. Usually the announcers microphone 8 feeds an amplifier, whichis connected in turn to the contact III of switch arm 6. Thus, closurelof switch 6-I0 permits the modulation appledto modulator 2 to be fromsolely source 8,' while source 3 is concurrently cut oir. A control toneis fed into amplifier 9 from pilot tone oscillator Il. The latteroperaies at a super-audible frequency, say 22 kc. Both oscillators ,iland Il. operate with constant aminvention may be carried into ingcurrent components by condenser 3|.

`anode end of resistor 3l is connected to a conplitude. It will now beseen that when the announcing switch 3+-I0 is closed the speech andcontrol tone me utilized as composite modulation. 'Ihe `reacts-ncedevice at 2 is varied in accordance with output of amplifier 9.v Sincethe channel is at least 150 kc. wide, the super-audible control tone isreadily utilized in thev transmission. The

- F. M. wave energy is amplified by power amplifier I2, and radiated bythe antenna I3. y

f course, the sources 3 and 8 may be respectively music and speech kfordifferent sequences oi! a long broadcast schedule. The sources may belocated in separate studios. and the switch deasoaova c J end connectedto the anode of diode rectifier 32, L

while the opposite end is connectedto the lower end of load resistor 33.The latter is bypassed by alternating current components by condenser34. 'Ihe lower end of resistor-33 is connected to the negative terminalof a source of high negative biasing potential 35 whose positiveterminal is grounded. The cathode end or resistor 33 is viceIIi--Ii--Ili maythenbe used as a change-over switch from one program toanother. At the receiver the collector I4, which may be a dipole, feedsthe collected FM wave energy to a radio frequency amplifier I5. Thelatter may include lone or more selector circuits each tuned to themean, or carrier, frequency of the collected wave energy. The converterI6 reduces the 'center frequency to an operating I. F. value, and thelatter may be 4.3 mc. After intermediate frequency (I. F.) amplificationat I1, thel energy is subjected to the action of an amplitude limiterI8. The latter functions to eliminate any amplitude modulation effectswhich may arise in the receiving system.

The FM detector I9 may be of any welll known form, and the function ofthe detector is to derive from the FM wave energy the modulation whichwas applied to the master oscillator at the connected by lead 50 to acontact 31.

The audio frequency amplifier 2l may have a gain control electrodethereof, such as the signal input grid, connected to the adjustablecontrol switch arm 39. Thev contact' 38 is provided in spaced,intermediate relation to contacts 33` and 31. Contact 38 is connected tothe negative terminal of negative biasing source 40, the latter havingits positive terminal grounded. Switch arm 33 is adjustable, and can beconnected in electrical contact with point 38, point 38 or point v 31.Switch 39 is, therefore, the announcement control switch." Assuming thatswitch arm 39 is in contact with point 38, then the audio amplifier 2|will be operating in normal fashion since 1 the source 40 applies normalbias to the amplithereafter. In this way the super-audible control ntone is prevented from passing through to the audio amplifier 2I. 22 and23 may be arranged in cascade with the output terminals of amplier '2l'.The output transformer of amplifier 23 may be connected to any desiredtype of reproducer. Those skilled in constructing networks I I to 23inclusive, and, therefore, they are schematically represented.

l The monitoring circuit comprises the bandpass filter 25 having itsinput terminals connected to the output terminals of detector I9 by apath 2l. In other words when the 22 irc.v control energy exists in theoutput of the detector I9, the energy is transmitted over path 24 tonlter 25. The nlter 25 may have a passband width which is relativelynarrow so that only the energy of superaudible frequency will pass tothe amplifier 26. After amplification the super-audible control energyis applied to a pair of transformers 21 and 28.

The primary windings of the two transformers may be arranged in seriesin the Plate Circuit 0f amplier 26. The secondary of transformer 21 hasone side connected to the cathode of diode rectier 29, while itsOpposite end is connected to one end of load resistor 30, which is alsoconnected to the negative terminal of bias source 40. The load resistor30 is bypassed for alternattact 33. The secondary of transformer 28 hasone Successive audio amplifiersy Theiler. In that case the modulationfrom either of sources 3 or 8 will be heard. This follows because thereis nocontrol applied to amplifier 2i, even though the control toneexists, on the carrier when the switch B-IIJ is closed.

If, now, the switch arm 39 is adjusted topolnt n 36, only. the 'programmodulation from source 3 will be heard and announcements from source 8will be deleted. 'I'his occurs because when switch 5-10 is closed, thecontrol tone is super- -posed on the carrier. At the receiver the recti4iler 29 recties the control tone energy, and provides a direct currentvoltage across resistor 30 whose magnitude is suillciently high vto biasaudio amplifier 2| to cut-off. vAs'soon as the switch 6-I0 is open, andswitch -3-5 is closed, the program from source 3 is received, but nocontrol action is'applied to amplier 2| from rectifier l 29, since vnocontrol tone is applied to the carrier. In other words, when-switch39-36 is closed, the receiver automatically will be non-responsive tothat modulation source which is applied to the carrier concurrently withthe monitor tone.

. the art are fully acquainted with the manner of If now the switch arm39 is shifted so as to close switch 39-31 onlyfthe announcements fromlmicrophone 8 will be heard, andthe receiver will not be responsive whenswitch 6-5 is closed at the transmitter to apply modulation frommicrophone 3 on the carrier. This follows from the fact that normallythe negative biasing source 35 cuts off amplifier 2|. When, however,modulation is applied from source 8 concurrently with the pilot tone,then diode rectifier 32will develop direct current voltage acrossresistor 33which will be applied in a polarity sense such as to opposethe biasing source 35. The amplier'ZI is, therefore, rendered operative.However, the receiver will only be reproducing the modulation fromsource 8. Hence, the receiver now automatically responds solely tomodulation source-8, but does not respond to the other of themodulationv sources. From a generic viewpoint, therey fore, there hasbeen provided a selective switching mechanism which enables the samemonitor tone of super-audible frequency selectively to permit responseto one modulation source while prevent response to the modulation sourcecombined with the control -tone while permitting reannouncements may beprovided, instead of complete elimination of either. In that way,vforexample, the speech sequences could be at very low level, while themusic periods would be of normal level, orr the reverse could be had.

The super-audible control tone energy may, also, be utilized to provideacoustic compensation control and/or fidelity control. For either ofthese functions the direct current voltage developed across resistor 33by rectifier 32 may be used. Acoustic compensation control is readilyprovided by connecting the plate circuit of a control tube 4| to thegrid circuito! audio amplifier 22 through a path including condenser 42and coil 43 in series. The plate of tube 4i may be connected to anydesired source of positive potential through a proper choke coil. Thecathode of tube 4| may be connected to ground through any desiredbiasing means, such asf shown.

The plate to cathode impedance of tube 4I is regulated by connecting thecontrol grid thereof to lead 50 through a switch 4544. The choke coil 43has a low impedance to low audio frequencies, while condenser 42 has alow impedance to high audio frequencies. Hence, when switch 45-44 isclosed, high negative bias from source 35 biases tube 4| to cut-off;This is the condition when no modulation is being transmitted fromsource 8. However, when switch E-IU is closed and modulation fromsources 8 and Il are applied to the carrier, rectifier 32 will functionto render tube 4i conductive. means that the low and high audio notesare bypasse-d from the grid circuit of ampliiier 22. Of course, when theswitch 45 is adjusted to the free contact, no control is applied to tube22.

The fidelity control is provided by a tube 41 which is constructed inthe same manner as the acoustic compensation control. Therey is thisdifference: the condenser 46, which has a low impedance to high audiofrequencies, is arranged in series between the plate of tube 41 and thegrid circuit of amplifier tube 23. Switch arm 49 is connected to lead50, while the contact 48 is connected to the control grid of tube l4'1.When switch 49-48 is closed, and no control tone energy exists on thecarrier, the tube 41 is cut oil.

Thisl v However, when speech from source 8 is applied to the carrier,the control tone energy is rectified and overcomes the biasing source3B. This results in bypassing of the higher audio frequencies.Accordingly, fidelity of reproduction is limited on speech so that straynoise is reduced. It will be understood that the switch arms 39, 45 and49 are to be adjusted in any desired manner, or sequence. In such casewhere the microphone 8 is located in a studio where speech programs areconstantly delivered, the switch 49-48 is closed so that whenthemicrophone 8 is active in delivering speech to the carrier, therewill automatically be developed a limited fidelity of reproduction forthe receiver.

WhileI have indicated and described several systems for carrying myinvention into eiect, it will be apparent to one skilled in the art thatmy invention is by no means limited to the particular organizationsshown and described, but that many modifications may be made withoutdeparting from the scope of my invention.

What I claim is:

In a frequency modulation receiver oi' the type adapted to receivefrequency modulated carrier waves provided with a special controlfrequency modulation component representative of a desired conditioningof the receiver; lthe improvement comprising a detector at the receiver-to produce the modulation signals ofthe received waves, means forfiltering from the signals current of the special control frequency,means for utilizing the modulation signals, a source of volt age forrendering said utilizing means operative, a rectifier coupled to saidfiltering means, and responsive to said special control frequencycurrent, to overcome the eil'ect of said voltage source, a secondvoltage source capable of rendering said utilizing means ineiiective, asecond rectifier coupled to said filtering means for deriving from thecontrol current a voltage to overcome the effect of said second voltagesource, and means for selectively connecting in circuit Iwith theutilizing means either of said rectiiiers and its associated one of saidtwo voltage sources.

WINFIELDR Kocr'r.

